Moog 930 Power Supply

The System 55 uses a large 930 power supply that outputs +/-15 volts at 5A, +12V at 5A, and -6V at 8A.  There are top holes for the voltage adjustments.  The over voltage protection (OVP) and current limit adjustments are inside under the case.


The AC mains input is the lower Molex connector and the primaries can be switched for various mains voltages.  The DC outputs and sense is the upper Molex connector.  The pins are well marked.


Inside is the main transformer and four separate power supply boards.


The output wiring consists of +. -, and sense leads that route along the inside front.


The transformer secondary voltages run along the inside rear to the four PCBs.



Although the power supply is Moog, it is built using four OEM Powertec linear supplies designed with the LM723 regulator.  Each floating supply has an independent + and - sense.  The +15V, +12V, and -15V use identical 22B-300 supplies.  The -6V uses a 22B-100 which has a few part differences including larger filter capacitor values.  This is an original +15V power supply PCB.


I replaced the 6 capacitors with their nearest equivalent Nichicon and polished the push terminals, screw terminals, and fuse holder which had corroded.  The +12V power supply terminals had corroded quite badly and I needed to expose fresh metal and resolder them.

I noted a potential failure mode with the large capacitor.  It is held by a nylon tie strap and can shift forwards and backwards.  If it shifts backwards the case could short to the fuse terminal and is insulated only by the thin plastic covering.  The new capacitors are shorter so really can't shift but I used silicone adhesive to fasten them to the PCB anyways.  This is a restored +15V PCB.